Coin cell battery energy: tips on how to maintain it?
As hackers, we frequently contemplate the enjoyable elements of a design first, then take into consideration tips on how to energy it later. Perhaps it is pure to depart the boring, known-ish stuff till later, but when you aren’t getting this elementary half settled, you do not have a venture.
For actually low-power functions, a coin cell (CR2032 or CR2016) battery is usually a nice selection, however holding them means one other part in your BOM, extra soldering, and an extra level of failure. Or does it? As I am going to define on this put up, a correctly fashioned PCB footprint can really act because the holder itself, eliminating a part and its meeting. Whether or not or not this decreased the possibility of failure continues to be an open query, since PCBs can break or just bend over time.
Coin cell battery cutout choices
In order to not bury the lede – or lead– beneath are hyperlinks to a number of of my PCB coin cell holder designs:
- LED-No-Solder – an early experiment with PCB coin cell holding
- Transistor-Nightlight – light-sensitive LED illumination
- Jeremy Prepare dinner enterprise card – PCB card illuminates when pressed
Nominally, such designs use a 0.8mm thick PCB, although different thicknesses also can work. In the event you favor to purchase an instance of this battery holding “tech,” a number of of my designs are out there on Tindie.
The above information provide you with lots to experiment with, however learn on for a couple of extra necessary factors that may lower down in your growth time. Based on the LED-No-Solder GitHub web page, I have been engaged on this “simplified” battery holder for at the very least two years.
Inspiration and early experiments
I am not the primary to strive utilizing deformed PCBs as coin cell holders, although I am most likely near the highest for variety of makes an attempt. This 2017 put up by Brian McEvoy makes use of an (even thinner) 0.6mm PCB for a blinky enterprise card battery holder, as does this considerably extra difficult LED matrix card by Dennis Kaandorp. To not be omitted, I ultimately made my very own light-up enterprise card as linked above.
My first strive at this no-components design got here – as detailed right here – within the type of the “creatively” named LED-No-Solder beneath. Its footprint permits you to connect each an LED and a coin cell battery to the 0.8mm PCB with out solder, making what quantities to a glorified throwie.
Contact issues = button and vibration sensor?
The center “fork” within the LED-No-Solder contacts the detrimental CRxx pad, and its conductive floor extends round 6mm from the tip. This design ensures that this conductor cannot contact the vertical portion of the optimistic battery terminal. Nonetheless, what typically occurs is that it touches the protruding detrimental edge the place there isn’t a conductive pad on the PCB. The center of the fork is subsequently angled so that there’s a slight hole on the finish and no connection is made – and it would not have touched the optimistic terminal anyway.
The upside to this example is that the center fork can be utilized as both a hair-trigger momentary button, and even as a vibration sensor. I took benefit of this property to make the LightStrum light-up choose beneath. Whereas it appears to be like very cool, its comparatively massive measurement makes it considerably tough to make use of.
If you need strong contact as a substitute of a button/sensor, the center fork merely must be prolonged to the outer diameter of the coin cell, as proven beneath. My paranoia about doubtlessly connecting to the optimistic aspect seems to be unwarranted. With an elongated center contact, my work-in-progress Transistor Night time Gentle design produces a strong connection.
1 / 2 • Elongated center fork contact for strong connection
What about customary (1.6mm) PCBs?
Though most quick-turn board homes will get you thinner 0.8mm PCBs with out a lot of a trouble, they don’t seem to be as frequent as 1.6mm boards. Which means whereas the worth would possibly be the identical, there’s an excellent probability you will want to attend longer for the thin model of your design.
Based mostly on latest preliminary testing, my Transistor Night time Gentle design in 1.6mm thickness can maintain a CR2032 battery. The problem (and potential profit) is that it’s very arduous to get the battery in place, and correspondingly tough to get it out. This will hold issues safe, however for those who’re promoting a product involving this attachment methodology, I say be certain the customer is conscious of the required force-in course of!
After all, for those who actually don’t need the battery getting unfastened, you can too add a zip-tie to maintain it in place. Beneath is the most recent model of my Transistor Night time Gentle with zip-tie cutouts.
1.6mm PCB + zip-ties = most battery safety!
Technical apart: CR2032, CR2016 identify and dimensions
The primary two digits in CR2032 and CR2016 point out the diameter in mm (20mm). The final two are the thickness in tenths of a mm (32 = 3.2mm, 16 = 1.6mm). Naturally, the -32 cell sometimes has (loads) extra capability than its -16 counterpart.
The C in CR supposedly implies that the battery makes use of a Lithium battery chemistry, whereas the R signifies it’s spherical. I’ve additionally seen it acknowledged that CR stands for “coin cell,” which… solely type of is smart.
Is that this the way forward for coin cell holding? [Maybe… not]
As famous above by Mike Szczys on Bsky, this system is each interesting to hacking-minded folks.. and a little bit of an abuse of PCB designs. In my restricted testing, FR4 tends to evolve to the battery form over time, and whereas it nonetheless makes contact, I am unsure how properly it’s going to maintain onto its captured battery in years to come back.
Additionally, there’s the priority about children consuming these batteries (which – and that is simply my uninformed guess – I think has been unfairly lumped in with smaller listening to help batteries). This would possibly make a bigger entity hesitant to strive one thing new. So no, I do not see extra severe companies subbing out purpose-built battery holders for the PCB equal any time quickly.
On the identical time, hackers finally develop into enterprise leaders… or at the very least design influencers. As this idea will get confirmed out over time, folks would possibly come to belief it. Early testing exhibits the 1.6mm thick PCB design holds a CR2032 battery REALLY tightly. So who is aware of?
So for those who want a method to sneak a coin cell battery into your design with out bothering with a brand new part and its meeting, why not give this PCB-only answer a shot? After fairly a little bit of testing and iteration, I am a fan of this system!
Thanks for studying!
Thanks for studying the primary of my biweekly PCB Friday columns on Hackster. I am trying ahead to sharing extra PCB-related information and perception right here, and I hope you will observe alongside. You will discover my extra semi-technical musings at TechAdjacent.io, or e mail me at [email protected] if in case you have any solutions!
